1. Field of the Invention
The present invention relates to an electric actuator composed of an electric motor and a wave gear speed reducer connected to the electric motor.
2. Description of the Related Art
Hitherto, as a speed reducer, a wave gear type speed reducer has been known. This type of speed reducer includes an internal gear, a flexible annular external gear, and a wave generator which elliptically flexes the external gear to partially mesh the external gear with the internal gear. When an electric actuator is constructed by connecting a wave gear speed reducer to an electric motor, the wave generator is connected to a rotor of the electric motor, and either the internal gear or the external gear is secured to the case of the speed reducer. Thus, the other gear is rotatively slowed down as the wave generator rotates.
Conventionally, there has been known such an electric actuator with vane portions protrusively provided on a side surface of a wave generator, which side is adjacent to an electric motor, in order to cool the electric motor (refer to, for example, Japanese Patent Application Laid-Open No. H3-134345). In this electric actuator, a case of a speed reducer is extended toward the electric motor, and a stator of the electric motor is accommodated in the extended portion. Further, air is drawn in by the vane portions through an inner circumferential space of the stator (the space between the stator and a rotor) when the wave generator rotates, and then the air is blown toward an outer circumferential space of the stator thereby to air-cool the electric motor.
Desirably, the wave generator is also air-cooled because the wave generator becomes extremely hot due to the heat transferred from the external gear. However, according to the conventional example described above, only one side of the wave generator is positively air-cooled, which side is the side adjacent to the motor and has vane portions protrusively provided thereon. This arrangement makes it impossible to efficiently air-cool the wave generator. In addition, providing the vane portions protrusively on the side surface of the wave generator that is adjacent to the motor requires that the axial interval between the electric motor and the wave generator be increased to accommodate the protruding vane portions, inevitably resulting in an increased axial length of the electric actuator.